The present invention relates to a substrate conveying device for conveying a substrate such as a semiconductor wafer or an LCD glass substrate, between a cassette and a processing unit.
Generally, in the manufacture of a liquid crystal display, photolithography is employed so as to form a circuit, an electrode pattern or the like, on a substrate such as a glass substrate. In the photo-lithography, a series of processing steps, namely, the washing and drying of a substrate, the formation of a resist film on the substrate, the exposure of the resist film, the development, and the like, are carried out. In the processing device for carrying out these processing steps, substrates unloaded from a cassette placed in the cassette station are conveyed to the processing unit one by one while being held on an arm, and the substrates are subjected to the processing steps including washing, one after another. After that, the substrates which have been processed at each processing unit, are conveyed back into the cassette one by one while being held on the arm.
However, with regard to the upper surface of the arm for conveying substrates, in the case where the section of the upper surface, for supporting an unwashed substrate, and the section for supporting a washed substrate are used in common, the following problem easily occurs. That is, when an unwashed substrate is placed on the arm, a contaminant attached to the rear surface of the unwashed substrate is transferred onto the supporting section of the arm, and the transferred contaminant may then easily be further transferred via the arm onto the rear surface of a washed substrate, while conveying the washed substrate on the arm. In order to solve the described problem, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-152266 proposes a substrate conveying device. More specifically, in the substrate conveying device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-152266, a substrate unloading arm for taking out an unwashed substrate from a cassette, and conveying it to the washing unit, and a substrate loading arm for returning a substrate finished with washing in the washing unit, to the cassette are formed to be separate mechanisms, so as to avoid the reattachment of a contaminant.
However, in the substrate conveying device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-152266, which switches the substrate unloading arm and the processed substrate loading arm before and after washing, the entire arm is, for example, rotated, and therefore a wide space is required for fully moving the arm therein. Thus, the space of the device cannot be effectively used. Further, in the case where separate mechanisms are used as a substrate unloading arm, and a processed substrate loading arm as in the prior art substrate conveying device, separate loading and unloading arms must be prepared. Further, the drive mechanism for switching the loading and unloading arms is relatively large in size. Therefore, the entire structure becomes very complicated.